To conform a datetime field to just a date in your results and make it easy to group TIMESTAMP fields in the format “2015-12-25 12:23:23” so you can group any datetime value into actual days for daily reports, use “DATE_FORMAT” below:

DATE_FORMAT(datetime_field, '%Y-%m-%d')

In other words, if you have values from a SELECT statement that are date AND time stamps and you want to group all those values into the DAY, DATE_FORMAT converts the value for you.

So, with these values in the field “created_at”:

2015-03-01 11:11:11
2015-03-01 16:13:132015-03-01 19:01:01
2015-03-03 11:19:23

The following MySQL SELECT statement

SELECT DATE_FORMAT(created_at,'%Y-%m-%d') as created_at_days FROM your_table GROUP BY created_at_days

Will result in the following results:
2015-03-01
2015-03-03